This invention relates to an improvement on an operation prohibition device for a car loading audio instrument serving that the audio instrument is prohibited from being operated after it is stolen.
There has been proposed an operation prohibition device for a car loading audio instrument adapted to be unable to operate the audio instrument after it is disconnected from a car battery when it is stolen as disclosed by U.S. Pat. No. 4,710,907, for example, which is owned by the applicant. The U.S. Patent discloses a preset recitation code number being input in order to release the prohibition of operation of the audio instrument. Japanese Laying-open No. 60-138645 discloses that the recitation code number can be voluntarily set by an operator.
In such conventional devices, a program of a microcomputer for controlling an operation of the audio instrument requires to input a preset recitation code number when it is connected to an electric power. Since the audio instrument is disconnected from a car battery when it is stolen, the preset recitation code number has to be input before the audio instrument should be operated after it is again connected to a car battery.
Thus, it will be understood that the conventional audio instrument never stores a condition on which it is stolen, but is adapted to be prohibited from being operated when it is connected to the car battery, which occurs when it is stolen. However, this occurs not only when it is stolen, but also when it is initially mounted on a car or when it is again connected to the car battery after the car is checked or arranged. It will be noted that the recitation code number is essentially required when the audio instrument is again connected to the car battery after the car is checked or arranged.
In case that memories such as RAM used are of inexpensive volatile memory, a backup power source is required. Nonvolatile memories are more expensive than volatile ones.